Towhooks can malfunction as can any other mechanical device. Failure modes include uncommanded towline release and failure to release on command. Pilots must be prepared to abort any towed launch, whether ground or aerotow launch, at any time. Uncommanded towline release must be anticipated prior to every launch. Assess the wind and the airport environment, and then form an emergency plan prior to launch. If the towhook fails to release on command, try to release the towline again after removing tension from the line. Pull the release handle multiple times under varying conditions of towline tension. If the towline still cannot release, alert the towpilot and follow the emergency procedures described in Flight Maneuvers and Traffic Patterns.
Oxygen System Malfunctions
Oxygen is essential for flight safety at high altitude. If there is a suspected or detected failure in any component of the oxygen system, descend immediately to an altitude at which supplemental oxygen is not essential for continued safe flight. Remember, the first sign of oxygen deprivation is a sensation of apparent well-being. Problem-solving capability is diminished. If the pilot has been deprived of sufficient oxygen, even for a short interval, critical thinking capability has been compromised. Do not be lulled into thinking that the flight can safely continue at high altitude. Descend immediately and breathe normally at these lower altitudes for a time to restore critical oxygen to the bloodstream. Try to avoid hyperventilation, which prolongs the diminished critical thinking capability. Give enough time to recover critical thinking capability before attempting an approach and landing.
Drogue Chute Malfunctions
Some gliders are equipped with a drogue chute to add drag during the approach to land. This drag supplements the drag provided by the spoilers/dive brakes. The drogue chute is packed and stowed in the aft tip (tail cone) of the fuselage or in a special compartment in the base of the rudder. Drogue chutes are very effective when deployed properly and make steep approaches possible. The drogue chute is deployed and jettisoned on pilot command, such as would be necessary if the drag of the glider was so great that the glider would not otherwise have the range to make it to the spot of intended landing. There are several failure modes for drogue chutes. If it deploys accidentally or inadvertently during the launch, the rate of climb seriously degrades and it must be jettisoned. During the approach to land, an improperly packed or damp drogue chute may fail to deploy on command. If this happens, use the rudder to sideslip for a moment, or use the rudder to yaw the tail back and forth. Make certain to attain safe flying speed before attempting the slip or yawing motion. Either technique increases the drag force on the drogue chute compartment that pulls the parachute out of the compartment.
If neither technique deploys the drogue chute, the drogue canopy may deploy at a later time during the approach without further control input from the pilot. This results in a considerable increase in drag. If this happens, be prepared to jettison the drogue chute immediately if sufficient altitude to glide to the intended landing spot has not been reached.
Another possible malfunction is failure of the drogue chute to inflate fully. If this happens, the canopy “streams” like a twisting ribbon of nylon, providing only a fraction of the drag that would occur if the canopy had fully inflated. Full inflation is unlikely after streaming occurs, but if it does occur, drag increases substantially. It is much better to fly with a known drag configuration and adjust for it rather than be faced with a substantially increased drag coefficient at a place and time where a safe landing is no longer possible. If in doubt regarding the degree of deployment of the drogue chute, the safest option may be to jettison the drogue. Regardless of the malfunction type, the pilot should review approach and landing options for the drogue chute conditions.